1. Technical Field
The embodiments herein generally relate to communication systems, and more particularly to the field of estimating offsets in Integrated Services Digital Broadcasting (ISDB) systems.
2. Description of the Related Art
Timing and frequency offsets cause sub-carrier phase rotation in an orthogonal frequency division multiplexing (OFDM) system, and can degrade system performance and, therefore, lead to large bit error rates. Thus, it is important to estimate and compensate for the offsets. The mean phase rotation indicates the frequency offset while the slope of phase rotation across the sub-carriers indicates the timing offset. Thus, the frequency and timing offsets can be estimated based on the mean and the slope of sub-carrier phase rotations. To estimate the frequency and the timing offsets, the sub-carriers are divided into two sub-sets, each subset having equal number of sub-carriers. One of the sub-sets contain sub-carriers which are to the left side the sub-carrier whose frequency is equal to the radio frequency (RF) center frequency of the transmitting station; i.e., the DC sub-carrier. The other sub-set contains sub-carriers to the right side of the DC sub-carrier. Next, the mean of sub-carrier phase rotations of the two sets are computed. Then, the average of the two mean phase rotations are the estimate of the frequency offset, and the difference of the two mean phase rotations is the estimate of the time offset. In a traditional method, if one sub-carrier in one of the sub-sets is a bad sub-carrier, then such a bad sub-carrier is removed from the computation of the mean phase rotation of that sub-set, and nothing is done for the computation of the mean phase rotation of the other sub-set.
However, for systems like 1-segment ISDB-T and ISDB-TSB, since the numbers of sub-carriers are very small, removal of bad sub-carriers would introduce large noise in the estimations of timing and frequency offsets.